Temporal based subblock type motion vector predictor

ABSTRACT

Aspects of the disclosure provide a method and an apparatus including processing circuitry that determines, based on a syntax element in a coded video bitstream, that a current block in a current picture is coded in a subblock-based frame-rate up conversion (FRUC) mode and determines a corresponding block of the current block based on an offset vector indicating an offset between the current block and the corresponding block in the current picture. The processing circuitry determines a temporal motion vector predictor (TMVP) of a first subblock in the corresponding block based on a subblock in a forward reference picture and a subblock in a backward reference picture. The subblocks in the forward and backward reference pictures are matched using the subblock-based FRUC mode. The processing circuitry determines a TMVP of a subblock in the current block based on the TMVP of the first subblock in the corresponding block.

INCORPORATION BY REFERENCE

The present application claims the benefit of priority to U.S.Provisional Application No. 63/320,028, “TEMPORAL BASED SUBBLOCK TYPEMOTION VECTOR PREDICTOR” filed on Mar. 15, 2022, which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Uncompressed digital images and/or video can include a series ofpictures, each picture having a spatial dimension of, for example,1920×1080 luminance samples and associated chrominance samples. Theseries of pictures can have a fixed or variable picture rate (informallyalso known as frame rate), of, for example 60 pictures per second or 60Hz. Uncompressed image and/or video has specific bitrate requirements.For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080luminance sample resolution at 60 Hz frame rate) requires close to 1.5Gbit/s bandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of image and/or video coding and decoding can be thereduction of redundancy in the input image and/or video signal, throughcompression. Compression can help reduce the aforementioned bandwidthand/or storage space requirements, in some cases by two orders ofmagnitude or more. Although the descriptions herein use videoencoding/decoding as illustrative examples, the same techniques can beapplied to image encoding/decoding in similar fashion without departingfrom the spirit of the present disclosure. Both lossless compression andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transformprocessing, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding used in, for example, MPEG-2 generation codingtechnologies, does not use intra prediction. However, some newer videocompression technologies include techniques that attempt to performprediction based on, for example, surrounding sample data and/ormetadata obtained during the encoding and/or decoding of blocks of data.Such techniques are henceforth called “intra prediction” techniques.Note that in at least some cases, intra prediction is using referencedata only from the current picture under reconstruction and not fromreference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology, aspecific technique in use can be coded as a specific intra predictionmode that uses the specific technique. In certain cases, intraprediction modes can have submodes and/or parameters, where the submodesand/or parameters can be coded individually or included in a modecodeword, which defines the prediction mode being used. Which codewordto use for a given mode, submode, and/or parameter combination can havean impact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesof already available samples. Sample values of neighboring samples arecopied into the predictor block according to a direction. A reference tothe direction in use can be coded in the bitstream or may itself bepredicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from the 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes) defined inH.265. The point where the arrows converge (101) represents the samplebeing predicted. The arrows represent the direction from which thesample is being predicted. For example, arrow (102) indicates thatsample (101) is predicted from a sample or samples to the upper right,at a 45 degree angle from the horizontal. Similarly, arrow (103)indicates that sample (101) is predicted from a sample or samples to thelower left of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore, no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples indicated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from samplesto the upper right, at a 45 degree angle from the horizontal. In thatcase, samples S41, S32, S23, and S14 are predicted from the samereference sample R05. Sample S44 is then predicted from reference sampleR08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013).Currently, JEM/VVC/BMS can support up to 65 directions. Experiments havebeen conducted to identify the most likely directions, and certaintechniques in the entropy coding are used to represent those likelydirections in a small number of bits, accepting a certain penalty forless likely directions. Further, the directions themselves can sometimesbe predicted from neighboring directions used in neighboring, alreadydecoded, blocks.

FIG. 1B shows a schematic (110) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction direction bits that represent thedirection in the coded video bitstream can be different from videocoding technology to video coding technology. Such mapping can range,for example, from simple direct mappings, to codewords, to complexadaptive schemes involving most probable modes, and similar techniques.In most cases, however, there can be certain directions that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well working videocoding technology, be represented by a larger number of bits than morelikely directions.

Image and/or video coding and decoding can be performed usinginter-picture prediction with motion compensation. Motion compensationcan be a lossy compression technique and can relate to techniques wherea block of sample data from a previously reconstructed picture or partthereof (reference picture), after being spatially shifted in adirection indicated by a motion vector (MV henceforth), is used for theprediction of a newly reconstructed picture or picture part. In somecases, the reference picture can be the same as the picture currentlyunder reconstruction. MVs can have two dimensions X and Y, or threedimensions, the third being an indication of the reference picture inuse (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described with reference toFIG. 2 is a technique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry decodesprediction information of a current block in a current picture from acoded video bitstream. The prediction information indicating asubblock-based frame-rate up conversion (FRUC) (also referred to as asubblock-based FRUC mode). The processing circuitry determines acorresponding block of the current block based on an offset vector. Theoffset vector indicates an offset between the current block and thecorresponding block in the current picture. The processing circuitrydetermines a temporal motion vector predictor (TMVP) of a first subblockin the corresponding block based on a subblock in a forward referencepicture of the current picture and a subblock in a backward referencepicture of the current picture. The subblock in the forward referencepicture and the subblock in the backward reference picture are matchedusing the subblock-based FRUC. The processing circuitry determines,based on the TMVP of the first subblock in the corresponding block, aTMVP of a subblock in the current block.

In an example, the processing circuitry determines the TMVP of thesubblock in the current block as the TMVP of the first subblock in thecorresponding block.

In an example, the processing circuitry determines a motion vector (MV)of the TMVP of the subblock in the current block as a vector sum of theoffset vector and a respective MV of the TMVP of the first subblock inthe corresponding block.

In an example, the offset vector is zero.

In an example, the processing circuitry receives an index in the codedvideo bitstream and determines the offset vector from a predefinedoffset vector list based on the index.

In an example, the offset vector is signaled in the coded videobitstream.

In an example, the processing circuitry determines a TMVP of a secondsubblock in the corresponding block based on the TMVP of the firstsubblock in the corresponding block in response to the TMVP of thesecond subblock not being determined by the subblock-based FRUC. Thesecond subblock neighbors the first subblock.

In an example, the processing circuitry determines the TMVP of the firstsubblock in the corresponding block based on a motion vector between thesubblock in the forward reference picture and the subblock in thebackward reference picture. The motion vector passes through one of: acenter position, a top-left position, a top-right position, abottom-left position, or a bottom-right position in the first subblockin the corresponding block.

In an example, a picture order count (POC) of the forward referencepicture is less than a POC of the current picture and a POC of thebackward reference picture is larger than the POC of the currentpicture.

In an example, a subblock merge candidate list includes a subblock-basedtemporal motion vector prediction (SbTMVP) candidate and a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The processing circuitry reconstructs the current blockbased on the FRUC-based subblock merge candidate in response to asubblock merge index indicating the FRUC-based subblock merge candidate.

In an example, a subblock merge candidate list includes a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The subblock merge candidate list does not include asubblock-based temporal motion vector prediction (SbTMVP) candidate. Theprocessing circuitry reconstructs the current block based on theFRUC-based subblock merge candidate in response to a subblock mergeindex indicating the FRUC-based subblock merge candidate.

If a FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block is available, a subblock merge candidatelist includes the FRUC-based subblock merge candidate and does notinclude a subblock-based temporal motion vector prediction (SbTMVP)candidate. If the FRUC-based subblock merge candidate is not available,the subblock merge candidate list includes the SbTMVP candidate.

In an example, a pre-defined subblock size is N×N luma samples. If awidth W of the current block is smaller than N and a height H of thecurrent block is greater than or equal to N, the processing circuitrypartitions the current block into subblocks having a subblock width of Wand a subblock height of N. If H is smaller than N and W is greater thanor equal to N, the processing circuitry partitions the current blockinto the subblocks having the subblock width of N and the subblockheight of H.

In an embodiment, the processing circuitry decodes predictioninformation of a current block in a current picture from a coded videobitstream. The prediction information indicates a subblock-based FRUC.The processing circuitry determines an initial temporal motion vectorpredictor (TMVP) of a first subblock in the current block based on asubblock in a forward reference picture of the current picture and asubblock in a backward reference picture of the current picture. Thesubblock in the forward reference picture and the subblock in thebackward reference picture are matched based on the subblock-based FRUC.The processing circuitry determines, based on the initial TMVP of thefirst subblock in the current block and a motion vector offset (MVO), aTMVP of the first subblock in the current block.

In an example, the processing circuitry determines a motion vector (MV)of the TMVP of the first subblock in the current block as a vector sumof the MVO and a respective MV of the TMVP of the first subblock in thecurrent block.

In an example, the processing circuitry receives an index in the codedvideo bitstream and determines the MVO from a predefined MVO list basedon the index.

In an example, the MVO is signaled in the coded video bitstream.

In an example, the processing circuitry determines an initial TMVP of asecond subblock in the current block based on the initial TMVP of thefirst subblock in the current block in response to the initial TMVP ofthe second subblock not being determined by the subblock-based FRUC. Thesecond subblock neighbors the first subblock.

In an example, a subblock merge candidate list includes a subblock-basedtemporal motion vector prediction (SbTMVP) candidate and a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The processing circuitry reconstructs the current blockusing the FRUC-based subblock merge candidate in response to a subblockmerge index indicating the FRUC-based subblock merge candidate.

In an example, a subblock merge candidate list includes a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The subblock merge candidate list does not include asubblock-based temporal motion vector prediction (SbTMVP) candidate. Theprocessing circuitry reconstructs the current block using the FRUC-basedsubblock merge candidate in response to a subblock merge indexindicating the FRUC-based subblock merge candidate.

In an embodiment, the coded video bitstream comprising the currentpicture is received. The current picture includes the current block, andthe current block includes a plurality of subblocks. That the currentblock including the plurality of subblocks is coded in thesubblock-based FRUC mode can be determined based on a syntax element inthe coded video bitstream.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the methodsfor video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 shows an example of a current block (201) and surroundingsamples.

FIG. 3 is a schematic illustration of an exemplary block diagram of acommunication system (300).

FIG. 4 is a schematic illustration of an exemplary block diagram of acommunication system (400).

FIG. 5 is a schematic illustration of an exemplary block diagram of adecoder.

FIG. 6 is a schematic illustration of an exemplary block diagram of anencoder.

FIG. 7 shows a block diagram of an exemplary encoder.

FIG. 8 shows a block diagram of an exemplary decoder.

FIG. 9 shows positions of spatial merge candidates according to anembodiment of the disclosure.

FIG. 10 shows candidate pairs that are considered for a redundancy checkof spatial merge candidates according to an embodiment of thedisclosure.

FIG. 11 shows exemplary motion vector scaling for a temporal mergecandidate.

FIG. 12 shows exemplary candidate positions for a temporal mergecandidate of a current coding unit.

FIGS. 13-14 show an exemplary subblock-based temporal motion vectorprediction (SbTMVP) process used in an SbTMVP mode.

FIGS. 15A-15B show an exemplary SbTMVP process used in an SbTMVP mode.

FIG. 16A shows examples of two kinds of motion estimation (ME) includinga unidirectional ME and a bidirectional ME.

FIG. 16B-16C shows examples of unidirectional motion vector (MV)estimation and bidirectional MV estimation.

FIGS. 17A-17C show a frame rate up-conversion (FRUC)-based subblocktemporal motion vector prediction (TMVP) mode.

FIGS. 18A-18B show an example of a FRUC-based subblock TMVP mode.

FIG. 19 shows an example of a FRUC-based subblock TMVP mode.

FIG. 20 shows a flow chart outlining an encoding process according tosome embodiment of the disclosure.

FIG. 21 shows a flow chart outlining a decoding process according tosome embodiment of the disclosure.

FIG. 22 shows a flow chart outlining an encoding process according tosome embodiment of the disclosure.

FIG. 23 shows a flow chart outlining a decoding process according tosome embodiment of the disclosure.

FIG. 24 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates an exemplary block diagram of a communication system(300). The communication system (300) includes a plurality of terminaldevices that can communicate with each other, via, for example, anetwork (350). For example, the communication system (300) includes afirst pair of terminal devices (310) and (320) interconnected via thenetwork (350). In the FIG. 3 example, the first pair of terminal devices(310) and (320) performs unidirectional transmission of data. Forexample, the terminal device (310) may code video data (e.g., a streamof video pictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data, for example, during videoconferencing.For bidirectional transmission of data, in an example, each terminaldevice of the terminal devices (330) and (340) may code video data(e.g., a stream of video pictures that are captured by the terminaldevice) for transmission to the other terminal device of the terminaldevices (330) and (340) via the network (350). Each terminal device ofthe terminal devices (330) and (340) also may receive the coded videodata transmitted by the other terminal device of the terminal devices(330) and (340), and may decode the coded video data to recover thevideo pictures and may display video pictures at an accessible displaydevice according to the recovered video data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) are respectively illustrated as servers, personal computers andsmart phones but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example of an application for the disclosedsubject matter, a video encoder and a video decoder in a streamingenvironment. The disclosed subject matter can be equally applicable toother video enabled applications, including, for example, videoconferencing, digital TV, streaming services, storing of compressedvideo on digital media including CD, DVD, memory stick and the like, andso on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows an exemplary block diagram of a video decoder (510). Thevideo decoder (510) can be included in an electronic device (530). Theelectronic device (530) can include a receiver (531) (e.g., receivingcircuitry). The video decoder (510) can be used in the place of thevideo decoder (410) in the FIG. 4 example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In an embodiment, one coded videosequence is received at a time, where the decoding of each coded videosequence is independent from the decoding of other coded videosequences. The coded video sequence may be received from a channel(501), which may be a hardware/software link to a storage device whichstores the encoded video data. The receiver (531) may receive theencoded video data with other data, for example, coded audio data and/orancillary data streams, that may be forwarded to their respective usingentities (not depicted). The receiver (531) may separate the coded videosequence from the other data. To combat network jitter, a buffer memory(515) may be coupled in between the receiver (531) and an entropydecoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) is part of the video decoder(510). In others, it can be outside of the video decoder (510) (notdepicted). In still others, there can be a buffer memory (not depicted)outside of the video decoder (510), for example to combat networkjitter, and in addition another buffer memory (515) inside the videodecoder (510), for example to handle playout timing. When the receiver(531) is receiving data from a store/forward device of sufficientbandwidth and controllability, or from an isosynchronous network, thebuffer memory (515) may not be needed, or can be small. For use on besteffort packet networks such as the Internet, the buffer memory (515) maybe required, can be comparatively large and can be advantageously ofadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI) messages or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by subgroup controlinformation parsed from the coded video sequence by the parser (520).The flow of such subgroup control information between the parser (520)and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform unit(551) can pertain to an intra coded block. The intra coded block is ablock that is not using predictive information from previouslyreconstructed pictures, but can use predictive information frompreviously reconstructed parts of the current picture. Such predictiveinformation can be provided by an intra picture prediction unit (552).In some cases, the intra picture prediction unit (552) generates a blockof the same size and shape of the block under reconstruction, usingsurrounding already reconstructed information fetched from the currentpicture buffer (558). The current picture buffer (558) buffers, forexample, partly reconstructed current picture and/or fully reconstructedcurrent picture. The aggregator (555), in some cases, adds, on a persample basis, the prediction information the intra prediction unit (552)has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensated,block. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520). Videocompression can also be responsive to meta-information obtained duringthe decoding of previous (in decoding order) parts of the coded pictureor coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology or a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows an exemplary block diagram of a video encoder (603). Thevideo encoder (603) is included in an electronic device (620). Theelectronic device (620) includes a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in the place of thevideo encoder (403) in the FIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired. Enforcing appropriate coding speed is one function of acontroller (650). In some embodiments, the controller (650) controlsother functional units as described below and is functionally coupled tothe other functional units. The coupling is not depicted for clarity.Parameters set by the controller (650) can include rate control relatedparameters (picture skip, quantizer, lambda value of rate-distortionoptimization techniques, . . . ), picture size, group of pictures (GOP)layout, maximum motion vector search range, and so forth. The controller(650) can be configured to have other suitable functions that pertain tothe video encoder (603) optimized for a certain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create. The reconstructed sample stream (sample data)is input to the reference picture memory (634). As the decoding of asymbol stream leads to bit-exact results independent of decoder location(local or remote), the content in the reference picture memory (634) isalso bit exact between the local encoder and remote encoder. In otherwords, the prediction part of an encoder “sees” as reference picturesamples exactly the same sample values as a decoder would “see” whenusing prediction during decoding. This fundamental principle ofreference picture synchronicity (and resulting drift, if synchronicitycannot be maintained, for example because of channel errors) is used insome related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

In an embodiment, a decoder technology except the parsing/entropydecoding that is present in a decoder is present, in an identical or asubstantially identical functional form, in a corresponding encoder.Accordingly, the disclosed subject matter focuses on decoder operation.The description of encoder technologies can be abbreviated as they arethe inverse of the comprehensively described decoder technologies. Incertain areas a more detail description is provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture memory (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by applying lossless compression to the symbolsaccording to technologies such as Huffman coding, variable lengthcoding, arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video encoder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions, are performedin the unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows an exemplary diagram of a video encoder (703). The videoencoder (703) is configured to receive a processing block (e.g., aprediction block) of sample values within a current video picture in asequence of video pictures, and encode the processing block into a codedpicture that is part of a coded video sequence. In an example, the videoencoder (703) is used in the place of the video encoder (403) in theFIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes an inter encoder(730), an intra encoder (722), a residue calculator (723), a switch(726), a residue encoder (724), a general controller (721), and anentropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also generate intraprediction information (e.g., an intra prediction direction informationaccording to one or more intra encoding techniques). In an example, theintra encoder (722) also calculates intra prediction results (e.g.,predicted block) based on the intra prediction information and referenceblocks in the same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information in the bitstream according to a suitablestandard, such as the HEVC standard. In an example, the entropy encoder(725) is configured to include the general control data, the selectedprediction information (e.g., intra prediction information or interprediction information), the residue information, and other suitableinformation in the bitstream. Note that, according to the disclosedsubject matter, when coding a block in the merge submode of either intermode or bi-prediction mode, there is no residue information.

FIG. 8 shows an exemplary diagram of a video decoder (810). The videodecoder (810) is configured to receive coded pictures that are part of acoded video sequence, and decode the coded pictures to generatereconstructed pictures. In an example, the video decoder (810) is usedin the place of the video decoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode) and prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively. Thesymbols can also include residual information in the form of, forexample, quantized transform coefficients, and the like. In an example,when the prediction mode is inter or bi-predicted mode, the interprediction information is provided to the inter decoder (880); and whenthe prediction type is the intra prediction type, the intra predictioninformation is provided to the intra decoder (872). The residualinformation can be subject to inverse quantization and is provided tothe residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual informationfrom the frequency domain to the spatial domain. The residue decoder(873) may also require certain control information (to include theQuantizer Parameter (QP)), and that information may be provided by theentropy decoder (871) (data path not depicted as this may be low volumecontrol information only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual information as output by the residue decoder (873)and the prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block, that may bepart of the reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Various inter prediction modes can be used in VVC. For aninter-predicted CU, motion parameters can include MV(s), one or morereference picture indices, a reference picture list usage index, andadditional information for certain coding features to be used forinter-predicted sample generation. A motion parameter can be signaledexplicitly or implicitly. When a CU is coded with a skip mode, the CUcan be associated with a PU and can have no significant residualcoefficients, no coded motion vector delta or MV difference (e.g., MVD)or a reference picture index. A merge mode can be specified where themotion parameters for the current CU are obtained from neighboringCU(s), including spatial and/or temporal candidates, and optionallyadditional information such as introduced in VVC. The merge mode can beapplied to an inter-predicted CU, not only for skip mode. In an example,an alternative to the merge mode is the explicit transmission of motionparameters, where MV(s), a corresponding reference picture index foreach reference picture list and a reference picture list usage flag andother information are signaled explicitly per CU.

In an embodiment, such as in VVC, VVC Test model (VTM) referencesoftware includes one or more refined inter prediction coding tools thatinclude: an extended merge prediction, a merge motion vector difference(MMVD) mode, an adaptive motion vector prediction (AMVP) mode withsymmetric MVD signaling, an affine motion compensated prediction, asubblock-based temporal motion vector prediction (SbTMVP), an adaptivemotion vector resolution (AMVR), a motion field storage ( 1/16th lumasample MV storage and 8×8 motion field compression), a bi-predictionwith CU-level weights (BCW), a bi-directional optical flow (BDOF), aprediction refinement using optical flow (PROF), a decoder side motionvector refinement (DMVR), a combined inter and intra prediction (CIIP),a geometric partitioning mode (GPM), and the like. Inter predictions andrelated methods are described in details below.

Extended merge prediction can be used in some examples. In an example,such as in VTM4, a merge candidate list is constructed by including thefollowing five types of candidates in order: spatial motion vectorpredictor(s) (MVP(s)) from spatial neighboring CU(s), temporal MVP(s)from collocated CU(s), history-based MVP(s) (HMVP(s)) from afirst-in-first-out (FIFO) table, pairwise average MVP(s), and zeroMV(s).

A size of the merge candidate list can be signaled in a slice header. Inan example, the maximum allowed size of the merge candidate list is 6 inVTM4. For each CU coded in the merge mode, an index (e.g., a mergeindex) of a best merge candidate can be encoded using truncated unarybinarization (TU). The first bin of the merge index can be coded withcontext (e.g., context-adaptive binary arithmetic coding (CABAC)) and abypass coding can be used for other bins.

Some examples of a generation process of each category of mergecandidates are provided below. In an embodiment, spatial candidate(s)are derived as follows. The derivation of spatial merge candidates inVVC can be identical to that in HEVC. In an example, a maximum of fourmerge candidates are selected among candidates located in positionsdepicted in FIG. 9 . FIG. 9 shows positions of spatial merge candidatesaccording to an embodiment of the disclosure. Referring to FIG. 9 , anorder of derivation is B1, A1, B0, A0, and B2. The position B2 isconsidered only when any CU of positions A0, B0, B1, and A1 is notavailable (e.g., because the CU belongs to another slice or anothertile) or is intra coded. After a candidate at the position A1 is added,the addition of the remaining candidates is subject to a redundancycheck which ensures that candidates with same motion information areexcluded from the candidate list so that coding efficiency is improved.

To reduce computational complexity, not all possible candidate pairs areconsidered in the mentioned redundancy check. Instead, only pairs linkedwith an arrow in FIG. 10 are considered and a candidate is only added tothe candidate list if the corresponding candidate used for theredundancy check does not have the same motion information. FIG. 10shows candidate pairs that are considered for a redundancy check ofspatial merge candidates according to an embodiment of the disclosure.Referring to FIG. 10 , the pairs linked with respective arrows includeA1 and B1, A1 and A0, A1 and B2, B1 and B0, and B1 and B2. Thus,candidates at the positions B1, A0, and/or B2 can be compared with thecandidate at the position A1, and candidates at the positions B0 and/orB2 can be compared with the candidate at the position B1.

In an embodiment, temporal candidate(s) are derived as follows. In anexample, only one temporal merge candidate is added to the candidatelist. FIG. 11 shows exemplary motion vector scaling for a temporal mergecandidate. To derive the temporal merge candidate of a current CU (1111)in a current picture (1101), a scaled MV (1121) (e.g., shown by a dottedline in FIG. 11 ) can be derived based on a co-located CU (1112)belonging to a collocated reference picture (1104). In an example, thecollocated reference picture (also referred to as the collocatedpicture) is a particular reference picture, for example, used fortemporal motion vector prediction. The collocated reference picture usedfor the temporal motion vector prediction can be indicated by areference index in a syntax, such as a high-level syntax (e.g., apicture header, a slice header).

A reference picture list used to derive the co-located CU (1112) can beexplicitly signaled in a slice header. The scaled MV (1121) for thetemporal merge candidate can be obtained as shown by the dotted line inFIG. 11 . The scaled MV (1121) can be scaled from the MV of theco-located CU (1112) using picture order count (POC) distances tb andtd. The POC distance tb can be defined to be the POC difference betweena current reference picture (1102) of the current picture (1101) and thecurrent picture (1101). The POC distance td can be defined to be the POCdifference between the collocated reference picture (1104) of theco-located picture (1103) and the co-located picture (1103). A referencepicture index of the temporal merge candidate can be set to zero.

FIG. 12 shows exemplary candidate positions (e.g., C0 and C1) for atemporal merge candidate of a current CU. A position for the temporalmerge candidate can be selected between the candidate positions C0 andC1. The candidate position C0 is located at a bottom-right corner of aco-located CU (1210) of the current CU. The candidate position C1 islocated at a center of the co-located CU (1210) of the current CU. If aCU at the candidate position C0 is not available, is intra coded, or isoutside of a current row of CTUs, the candidate position C1 is used toderive the temporal merge candidate. Otherwise, for example, the CU atthe candidate position C0 is available, intra coded, and in the currentrow of CTUs, the candidate position C0 is used to derive the temporalmerge candidate.

A merge with motion vector difference (MMVD) mode can be used for a skipmode or a merge mode with a motion vector expression method. Mergecandidate(s), such as used in VVC, can be reused in the MMVD mode. Acandidate can be selected among the merge candidates as a starting point(e.g., an MV predictor (MVP)), and can be further expanded by the MMVDmode. The MMVD mode can provide a new motion vector expression withsimplified signaling. The motion vector expression method includes thestarting point and an MV difference (MVD). In an example, the MVD isindicated by a magnitude (or a motion magnitude) of the MVD, and adirection (e.g., a motion direction) of the MVD.

The MMVD mode can use a merge candidate list, such as used in VVC. In anembodiment, only candidate(s) which are of a default merge type (e.g.,MRG_TYPE_DEFAULT_N) are considered for the MMVD mode. The starting pointcan be indicated or defined by a base candidate index (IDX). The basecandidate index can indicate the best candidate among the candidates(e.g., the base candidates) in the merge candidate list. Table 1 showsan exemplary relationship between the base candidate index and thecorresponding starting point. The base candidate index being 0, 1, 2, or3 indicates the corresponding starting point being a 1^(st) MVP, a2^(nd) MVP, a 3^(rd) MVP, or a 4^(th) MVP. In an example, if a number ofthe base candidate(s) is equal to 1, the base candidate IDX is notsignaled.

TABLE 1 Base candidate IDX Base candidate IDX 0 1 2 3 N^(th) MVP 1^(st)MVP 2^(nd) MVP 3^(rd) MVP 4^(th) MVP

A distance index can indicate motion magnitude information of the MVD,such as the magnitude of the MVD. For example, the distance indexindicates a distance (e.g., a pre-defined distance) from the startingpoint (e.g., the MVP indicated by the base candidate index). In anexample, the distance is one of a plurality of pre-defined distances,such as shown in Table 2. Table 2 shows an exemplary relationshipbetween the distance index and the corresponding distance (in units ofsamples or pixels). 1 pel in Table 2 is one sample or one pixel. Forexample, the distance index being 1 indicates the distance to be ½-pelor ½ samples.

TABLE 2 Distance IDX Distance IDX 0 1 2 3 4 5 6 7 Pixel 1/4-pel 1/2-pel1-pel 2-pel 4-pel 8-pel 16-pel 32-pel distance

A direction index can represent the direction of the MVD relative to thestarting point. The direction index can represent one of a plurality ofdirections, such as four directions as shown in Table 3. For example,the direction index being 00 indicates the direction of the MVD beingalong the positive x-axis.

TABLE 3 Direction IDX Direction IDX 00 01 10 11 x-axis + − N/A N/Ay-axis N/A N/A + −

An MMVD flag can be signaled after sending a skip and merge flag. If theskip and merge flag is true, the MMVD flag can be parsed. In an example,if the MMVD flag is equal to 1, MMVD syntaxes (e.g., including adistance index and/or a direction index) can be parsed. If the MMVD flagis not equal to 1, an AFFINE flag can be parsed. If the AFFINE flag isequal to 1, the AFFINE mode is used to code the current block. If theAFFINE flag is not equal to 1, a skip/merge index can be parsed for askip/merge mode, such as used in VTM.

FIGS. 13-14 show an example of a search process in the MMVD mode. Byperforming the search process, indices including a base candidate index,a direction index, and/or a distance index can be determined for acurrent block (1300) in a current picture (or referred to as a currentframe) (1301).

A first motion vector (MV) (1311) and a second MV (1321) belonging to afirst merge candidate are shown. The first merge candidate can be amerge candidate in a merge candidate list constructed for the currentblock (1300). The first and second MVs (1311) and (1321) can beassociated with two reference pictures (1302) and (1303) in referencepicture lists L0 and L1, respectively. Accordingly, two starting points(1411) and (1421) in FIGS. 13-14 can be determined at the referencepictures (1302) and (1303), respectively.

In an example, based on the starting points (1411) and (1421), multiplepredefined points (e.g., 1-12 shown in FIG. 14 ) extending from thestarting points (1411) and (1421) in vertical directions (represented by+Y, or −Y) or horizontal directions (represented by +X and −X) in thereference pictures (1302) and (1303) can be evaluated. In one example, apair of points mirroring each other with respect to the respectivestarting point (1411) or (1421), such as the pair of points (1414) and(1424), or the pair of points (1415) and (1425), can be used todetermine a pair of MVs (1314) and (1324) or a pair of MVs (1315) and(1325) which may form MV predictor (MVP) candidates for the currentblock (1300). The MVP candidates determined based on the predefinedpoints surrounding the starting points (1411) and/or (1421) can beevaluated. Referring to FIG. 13 , an MVD (1312) between the first MV(1311) and the MV (1314) has a magnitude of 1 S. An MVD (1322) betweenthe second MV (1321) and the MV (1324) has a magnitude of 1 S.Similarly, an MVD between the first MV (1311) and the MV (1315) has amagnitude of 2 S. An MVD between the second MV (1321) and the MV (1325)has a magnitude of 2 S.

In addition to the first merge candidate, other available or valid mergecandidates in the merge candidate list of the current block (1300) canalso be evaluated similarly. In one example, for a uni-predicted mergecandidate, only one prediction direction associated with one of the tworeference picture lists is evaluated.

In an example, based on the evaluations, a best MVP candidate can bedetermined. Accordingly, corresponding to the best MVP candidate, a bestmerge candidate can be selected from the merge list, and a motiondirection and a motion distance can also be determined. For example,based on the selected merge candidate and the Table 1, a base candidateindex can be determined. Based on the selected MVP, such as thatcorresponding to the predefined point (1415) (or (1425)), a directionand a distance (e.g., 2 S) of the point (1415) with respect to thestarting point (1411) can be determined. According to Table 2 and Table3, a direction index and a distance index can accordingly be determined.

As described above, two indices, such as a distance index and adirection index can be used to indicate an MVD in the MMVD mode.Alternatively, a single index can be used to indicate an MVD in the MMVDmode, for example, with a table that pairs the single index with theMVD.

To improve the coding efficiency and reduce the transmission overhead ofMV(s), a subblock level MV refinement can be applied to extend a CUlevel temporal motion vector prediction (TMVP). In an example, asubblock-based TMVP (SbTMVP) mode allows inheriting motion informationat a subblock-level from a collocated reference picture. As describedabove, the collocated reference picture can be indicated by a referenceindex in a syntax, such as a high-level syntax (e.g., a picture header,a slice header).

Each subblock of a current CU (e.g., a current CU with a large size) ina current picture can have respective motion information withoutexplicitly transmitting a block partition structure or the respectivemotion information. In the SbTMVP mode, motion information for eachsubblock can be obtained as follows, for example, in three steps. In thefirst step, a displacement vector (DV) of the current CU can be derived.The DV can indicate a block in the collocated reference picture, forexample, the DV points from the current block in the current picture tothe block in the collocated reference picture. Thus, the block indicatedby the DV is considered as being collocated with the current block andis referred to as a collocated block of the current block. In the secondstep, availability of an SbTMVP candidate can be checked and a centralmotion (e.g., a central motion of the current CU) can be derived. In thethird step, subblock motion information can be derived from acorresponding subblock in the collocated block using the DV. The threesteps can be combined into one or two steps, and/or an order of thethree steps may be adjusted.

Unlike TMVP candidate derivation which derives temporal MVs from acollocated block in a reference frame or a reference picture, in theSbTMVP mode, a DV (e.g., a DV derived from an MV of a left neighboringCU of the current CU) can be applied to locate a corresponding subblockin the collocated picture for each subblock in the current CU that is inthe current picture. If the corresponding subblock is not inter-coded,motion information of the current subblock can be set to be the centralmotion of the collocated block.

The SbTMVP mode can be supported by various video coding standardsincluding for example VVC. Similar to the TMVP mode, for example, inHEVC, in the SbTMVP mode, a motion field (also referred to as a motioninformation field, an MV field) in the collocated picture can be used toimprove MV prediction and a merge mode for CUs in the current picture.In an example, the same collocated picture used by the TMVP mode is usedin the SbTVMP mode. In an example, the SbTMVP mode differs from the TMVPmode in the following aspects: (i) the TMVP mode predicts motioninformation at the CU level while the SbTMVP mode predicts motioninformation at a sub-CU level; (ii) the TMVP mode fetches the temporalMVs from the collocated block in the collocated picture (e.g., thecollocated block is the bottom-right or a center block relative to thecurrent CU) while the SbTMVP mode can apply a motion shift beforefetching the temporal motion information from the collocated picture. Inan example, the motion shift used in the SbTMVP mode is obtained from anMV of one of spatial neighboring blocks of the current CU.

FIGS. 15A-15B show an exemplary SbTMVP process used in the SbTMVP mode.The SbTMVP process can predict MVs of sub-CUs (e.g., subblocks) within acurrent CU (e.g., a current block) (1501) in a current picture (1511),for example, in two steps. In the first step, a spatial neighbor (e.g.,A1) of the current block (1501) in FIGS. 15A-15B is examined. If thespatial neighbor (e.g., A1) has an MV (1521) that uses a collocatedpicture (1512) as a reference picture of the spatial neighbor (e.g.,A1), the MV (1521) can be selected to be a motion shift (or a DV) to beapplied to the current block (1501). If no such MV (e.g., an MV thatuses the collocated picture (1512) as a reference picture) isidentified, the motion shift or the DV can be set to a zero MV (e.g.,(0, 0)). In some examples, MV(s) of additional spatial neighbors, suchas A0, B0, B1, and the like are checked if no such MV is identified forthe spatial neighbor A1.

In the second step, the motion shift or the DV (1521) identified in thefirst step can be applied to the current block (1501) (e.g., the DV(1521) is added to coordinates of the current block) to obtain sub-CUlevel motion information (e.g., including MVs and reference indices)from the collocated picture (1512). In the example shown in FIG. 15B,the motion shift or the DV (1521) is set to be the MV of the spatialneighbor A1 (e.g., a block A1) of the current block (1501). For eachsub-CU or subblock (1531) in the current block (1501), motioninformation of a corresponding collocated block (1591) (e.g., motioninformation of the smallest motion grid that covers a center sample ofthe collocated block (1591)) in the collocated picture (1512) can beused to derive the motion information for the sub-CU or subblock (1531).After the motion information of the collocated sub-CU (1532) in thecollocated block (1591) is identified, the motion information of thecollocated sub-CU (1532) can be converted to the motion information(e.g., MV(s) and one or more reference indices) of the current sub-CU(1531) using a scaling method, such as in a similar way as the TMVPprocess used in HEVC, where temporal motion scaling is applied to alignreference pictures of temporal MVs to reference pictures of a currentCU.

The motion field of the current block (1501) derived based on the DV(1521) can include motion information of each subblock (1531) in thecurrent block (1501), such as MV(s) and one or more associated referenceindices. The motion field of the current block (1501) can also bereferred to as an SbTMVP candidate and corresponds to the DV (1521).

FIG. 15B shows an example of the motion field or the SbTMVP candidate ofthe current block (1501). The motion information of the subblock(1531(1)) that is bi-predicted includes a first MV, a first indexindicating a first reference picture in a reference picture list 0 (L0),a second MV and a second index indicating a second reference picture ina reference picture list 1 (L1). In an example, the motion informationof the subblock (1531(2)) that is un-predicted includes an MV and anindex indicating a reference picture in L0 or L1.

In an example, the DV (1521) is applied to a central position of thecurrent block (1501) to locate a displaced central position in thecollocated picture (1512). If a block including the displaced centralposition is not inter-coded, the SbTMVP candidate is considered notavailable. Otherwise, if a block (e.g., the collocated block (1591))including the displaced central position is inter-coded, the motioninformation of the central position of the current block (1501),referred to as central motion of the current block (1501), can bederived from motion information of the block including the displacedcentral position in the collocated picture (1512). In an example, ascaling process can be used to derive the central motion of the currentblock (1501) from the motion information of the block including thedisplaced central position in the collocated picture (1512). When theSbTMVP candidate is available, the DV (1521) can be applied to find thecorresponding subblock (1532) in the collocated picture (1512) for eachsubblock (1531) of the current block (1501). The motion information ofthe corresponding subblock (1532) can be used to derive the motioninformation of the subblock (1531) in the current block (1501), such asin the same way used to derive the central motion of the current block(1501). In an example, if the corresponding subblock (1532) is notinter-coded, the motion information of the current subblock (1531) isset to be the central motion of the current block (1501).

In some examples, such as in VVC, a combined subblock-based merge listwhich includes an SbTMVP candidate and affine merge candidate(s) is usedin the signaling of a subblock-based merge mode. The SbTMVP mode can beenabled or disabled by a sequence parameter set (SPS) flag. If theSbTMVP mode is enabled, the SbTMVP candidate (or the SbTMVP predictor)can be added as the first entry of the subblock-based merge listincluding subblock-based merge candidates, and followed by the affinemerge candidate(s). The size of the subblock-based merge list can besignaled in the SPS. In an example, the maximum allowed size of thesubblock-based merge list is 5 in VVC. In an example, multiple SbTMVPcandidates are included in the subblock-based merge list.

In some examples, such as in VVC, the sub-CU size used in the SbTMVPmode is fixed to be 8×8, such as used for the affine merge mode. In anexample, the SbTMVP mode is only applicable to a CU with both a widthand a height being larger than or equal to 8. The subblock size (e.g.,8×8) may be configurable to other sizes, such as 4×4 in an ECM softwaremodel use for exploration beyond VVC. In an example, multiple collocatedpictures, such as two collocated frames, are utilized to providetemporal motion information for the SbTMVP and/or the TMVP in the AMVPmode.

In related technologies, a frame rate up-conversion (FRUC) process canbe used in display to generate a high frame rate video based on a lowframe rate video. A FRUC process can be used to generate an interpolatedpicture or frame based on other pictures (e.g., a forward referencepicture and a backward reference picture) by using any suitable method,such as picture repetition, picture averaging, motion-compensation,and/or the like.

In an example, a FRUC process with motion-compensation is used todetermine an interpolated picture (or an interpolated frame), and can bereferred to as a motion-compensation FRUC (MC-FRUC). In MC-FRUC, objectmovement(s) can be used to generate an interpolated frame. MC-FRUC caninclude two steps, motion estimation (ME) and motion-compensatedinterpolation (MCI). Motion estimation can track motion trajectoriesbetween a forward reference frame and a backward reference frame. Motionvectors (MVs) can be generated in ME. An interpolated picture can begenerated based on the MVs in MCI.

Similar to the video coding, block-matching motion estimation (BM-ME)can be used in MC-FRUC. In MC-FRUC, an image can be divided into blocksand a movement or motion (e.g., a motion trajectory) of each block canbe detected according to the ME between a forward reference frame and abackward reference frame.

FIG. 16A shows examples of two kinds of ME including a unidirectional ME(also referred to as a unilateral ME) and a bidirectional ME (alsoreferred to as a bilateral ME) can be used in BM-ME. In FIG. 16A, afirst reference picture (e.g., a forward reference picture) (1602) and asecond reference picture (e.g., a backward reference picture) (1603) canbe used in motion estimation. The unidirectional ME can be used todetermine an MV (1621) of a block (1613) in the second reference picture(1603) by searching for a block (1612) in the first reference picture(1602) that matches with the block (1613). A block (1611) along a motiontrajectory (e.g., a translational motion from the block (1613) to theblock (1612)) can be located in a picture (e.g., an interpolatedpicture) (1601).

The bidirectional ME can be used to determine MVs (1631)-(1632) passingthrough the block (1611) in the picture (1601) using the temporalsymmetry between the blocks (1612)-(1613) in the first reference picture(1602) and the second reference picture (1603). In the bilateral ME, theblocks (1612)-(1613) are matched.

FIG. 16B shows examples of unidirectional MV estimation andbidirectional MV estimation. In the unidirectional MV estimation, thesecond reference picture (1603) can be divided into blocks (e.g.,non-overlapped blocks) that include the block (1613). A search range(1642) around an initial block in the first reference picture (1602) canbe determined. Each block within the search range (1642) in the firstreference picture (1602) can be compared with the block (1613). Adifference between the block (1613) and each block within the searchrange (1642) can be determined based on any suitable method, such assuch as a sum of absolute difference (SAD), a sum of absolutetransformed differences (SATD), sum of squared errors (SSE), a meanremoved SAD/SATD/SSE, a variance, a partial SAD, a partial SSE, apartial SATD, or the like. The block (1612) that has the leastdifference (e.g., the least SAD) with the block (1613) in the secondreference picture (1603) can be chosen and the MV (1621) that areassociated with the blocks (1612)-(1613) can be determined.

In an example, the MV (1621) indicates a motion (e.g., a translationalmotion or motion trajectory) between the (1612)-(1613). An MV of theblock (1611) can be estimated based on the MV (1621) that points to theblock (1611). In an example, an MV predictor (e.g., a temporal MVpredictor or TMVP) (1622) of the block (1611) is determined based on theMV (1621). For example, the MV (1621) can be temporally scaled todetermine the TMVP of the block (1611). If a first POC differencebetween the picture (1601) and the forward reference picture (1602) isequal to a second POC difference between the picture (1601) and thebackward reference picture (1603), the TMVP (1622) is one half of the MV(1621). Similarly, other TMVPs of blocks in the picture (1601) can bedetermined, and thus a first MV field of the picture (1601) thatindicates motion information (e.g., TMVPs) of the blocks in the picture(1601) can be determined using the unidirectional MV estimation.

A second MV field of the picture (1601) can be determined by startingfrom blocks in the forward reference picture (1602) and search forcorresponding matching blocks in the backward reference picture (1603),similarly as described above.

In some examples, a MV field of the picture (1601) is determined basedthe first MV field of the picture (1601) and the second MV field of thepicture (1601).

In an example of the bidirectional MV estimation, two unidirectional MVestimations can be used. A first unidirectional MV estimation isdescribed above in FIG. 16B where the block (1612) is determined fromthe block (1613), and the MV (1621) is determined based on the blocks(1612)-(1613). After the block (1612) is determined, a secondunidirectional MV estimation shown in FIG. 16C can start with the block(1612) to search for a corresponding block (1618) within a search range(1643) in the backward reference picture (1603) that matches with theblock (1612) using the unidirectional MV estimation described in FIG.16B. In an example, the corresponding block (1618) in the backwardreference picture (1603) is the block (1613). In another example, suchas shown in FIG. 16C, the corresponding block (1618) in the backwardreference picture (1603) is different from the block (1613). An MV(1623) can be determined based on the blocks (1612) and (1618). In anexample, Similarly, a TMVP that is an estimate to the MV of the block(1611) can be determined based on the MVs (1621) and (1623).

In another example of the bidirectional MV estimation, for the block(1611) in the picture (1601), a search within search ranges (1652) and(1653) in the forward reference picture (1602) and the backwardreference picture (1603), respectively, can be performed to determinethe MVs (1631)-1632) passing through the block (1611) in the picture(1601). For example, a block within the search range (1652) is comparedwith a block in the search range (1653). Similarly as described in theunidirectional MV estimation, a difference between the block within thesearch range (1652) and the block in the search range (1653) isdetermined. The blocks (1612)-(1613) that have the least difference(e.g., the least SAD) can be chosen and the MVs (1631)-(1632) can bedetermined. In an example, the MV (1631) is opposite to the MV (1632).In an example, the MV (1631) is not opposite to the MV (1632). TMVPs ofthe block (1611) can be determined based on the MVs (1631)-(1632). In anexample, the MV (1631) indicates the block (1613) from the block (1611)and the MV (1632) indicates the block (1612) from the block (1611), andthus the TMVPs of the block (1611) are determined from the MVs(1631)-(1632) without temporal scaling.

The motion information (e.g., MVs of blocks in the current picture) ofthe current picture can be determined (e.g., derived) using the FRUCmode instead of being signaled. In the FRUC mode, the motion informationof the current picture, such as motion information (e.g., MVs) of blocksin the current picture can be determined based on motion estimation thattracks motion trajectories between reference blocks in two respectivereference pictures, such as described in FIGS. 16B-16C. For example, inthe FRUC mode, motion information of a block (e.g., (1611)) in thecurrent picture (e.g., (1601)) is determined based on motion estimationthat tracks a motion trajectory between reference blocks (e.g.,(1612)-(1613)) in the two respective reference pictures (e.g.,(1602)-(1603)).

In some embodiments, such as in VVC and ECM, the SbTMVP mode may use aDV which is only derived from an MV of a neighboring CU of a current CU.Thus, motion information (e.g., inherited motion information) of theSbTMVP mode may not be efficient, for example, due to a weak spatialdomain relationship between the current CU and the neighboring CU.

The application describes embodiments related to the derivation of theSbTMVP by using FRUC.

According to an embodiment of the disclosure, blocks or subblocks in twopictures can be used to determine motion information of a first subblockin a current block in a current picture where the current block is codedwith inter prediction using a subblock-based mode. In an example, thetwo pictures are a forward reference picture (or a forward referenceframe) and a backward reference picture (or a backward reference frame)of the current picture. In an example, a picture order count (POC) ofone of the two pictures (e.g., the forward reference picture) is smallerthan a POC of the current picture, and a POC of another of the twopictures (e.g., the backward reference picture) is larger than the POCof the current picture. According to an embodiment of the disclosure,the motion information of the first subblock can be determined using asubblock-based FRUC, for example, implemented using the unidirectionalMV estimation(s) and/or the bidirectional MV estimation(s) describedabove.

FIGS. 17A-17C show a subblock-based FRUC or a subblock-based FRUC mode.A current block (1704) is in a current picture (1701). The current block(1704) can include multiple subblocks, such as (1711)-(1714). Thesubblocks (1711)-(1714) can have any suitable width N and any suitableheight M, such as N×M. N and M can be positive integers. In an example,one of N and M is 1, and the other of N and M is larger than 1. Thewidth N and the height M of the subblocks (1711)-(1714) can be identicalor different.

Referring to FIGS. 17A-17C, a corresponding block (1706) of the currentblock (1704) can be determined based on a first offset vector (e.g.,such as a first motion vector offset (MVO)) (1705) where the firstoffset vector (1705) can indicate an offset between the current block(1704) and the corresponding block (1706). In an example, the firstoffset vector (1705) is signaled for the current block (1704) and parsedto indicate the location of the corresponding block (1706) in thecurrent picture (1701). The corresponding block (1706) is in the currentpicture (1701). The corresponding block (1706) can include subblocks(1721)-(1724) that correspond to the subblocks (1711)-(1714),respectively.

Motion information of a subblock (e.g., (1721)) in the correspondingblock (1706) can be estimated or predicted based on a subblock (e.g.,(1741)) in a forward reference picture (1702) of the current picture(1701) and a corresponding subblock (e.g., (1731)) in a correspondingbackward reference picture (1703) of the current picture (1701) usingany suitable FRUC process, such as the unidirectional MV estimations(e.g., described in FIG. 16B) or the bidirectional MV estimations (e.g.,such as described in FIGS. 16B-16C). In an example, additionalunidirectional MV estimation(s) and/or additional bidirectional MVestimation(s) are performed based on additional forward referencepicture(s) and/or additional backward reference picture(s). In someexamples, the motion information of the subblock (e.g., (1721)) isdetermined based on respective motion information obtained fromunidirectional MV estimation(s) and/or bidirectional MV estimation(s).Motion information of other subblocks (e.g., (1722)-(1724)) in thecorresponding block (1706) can be determined similarly using the FRUCprocess.

In general, multiple subblocks in the forward reference picture (1702)and the backward reference picture (1703) can be used to determine(e.g., estimate) motion information of each subblock in thecorresponding block (1706). In an example, more than two subblocks inthe forward reference picture (1702) and the backward reference picture(1703) are used. Referring back to FIGS. 16B-16C, when twounidirectional MV estimations are used as a bidirectional MV estimation,three blocks (1612), (1613), and (1618) can be used where the blocks(1612)-(1613) are used to determine an MV and the blocks (1613) and(1618) are used to determine another MV.

In an example shown in FIG. 17A, the unidirectional MV estimation (e.g.,similar to that described in FIG. 16B) can be used to determine TMVPs(e.g., CorTMVPs) (1751)-1754) of the respective subblocks (1721)-(1724)in the corresponding block (1706). The TMVPs (1751)-(1754) associatedwith the corresponding block (1706) can be referred to as CorTMVPs. TheTMVPs (1751)-(1754) can be predictors of, or estimates to, therespective motion information (e.g., MVs) of the subblocks(1721)-(1724). In an example, the TMVPs (1751)-(1754) of the respectivesubblocks (1721)-(1724) are determined based on subblocks (1731)-(1734)in the backward reference picture (1703) and corresponding subblocks(1741)-(1744) in the forward reference picture (1702), respectively. Insome examples, other subblocks in the backward reference picture (1703)and the forward reference picture (1702) are used to determine the TMVPs(1751)-(1754).

In an example, multiple unidirectional MV estimations can be used todetermine the TMVPs (1751)-(1754) of the respective subblocks(1721)-(1724) in the corresponding block (1706).

In an example, the bidirectional MV estimation (e.g., such as describedin FIGS. 16B-16C) can be used to determine the TMVPs (1751)-(1754) ofthe respective subblocks (1721)-(1724) in the corresponding block(1706).

The TMVPs (1751)-(1754) of the respective subblocks (1721)-(1724) in thecorresponding block (1706) can be derived as described above. In FIG.17A, the TMVPs (1751)-(1754) are represented by arrows pointing from thesubblocks (1731)-(1734) in the backward reference picture (1703) to thesubblocks (1741)-(1744) in the forward reference picture (1702),respectively, for illustration purposes.

The TMVPs (1751)-(1754) of the respective subblocks (1721)-(1724) caninclude MVs for uni-prediction. FIG. 17B shows an example of the TMVPs(1751)-(1754) (e.g., indicating magnitudes and directions of the TMVPs(1751)-(1754)) of the respective subblocks (1721)-(1724) in thecorresponding block (1706). The TMVPs (1751)-(1754) of the respectivesubblocks (1721)-(1724) can be represented using (i) CorTMV_(L0)(xi, yi)or CorTMV_(L0,i) (e.g., MVs) that are associated with the forwardreference picture (1702) or (ii) CorTMV_(L1)(xi, yi) or CorTMV_(L1,i)(e.g., MVs) that are associated with the backward reference picture(1703). A coordinate (xi, yi) can indicate an ith subblock in thecorresponding block (1706) at a location (xi, yi). A parameter i can bean integer, for example, i being 0, 1, 2, or 3 refers to the subblocks(1721)-(1724) in the corresponding block (1706), respectively.

In an example, a unidirectional MV estimation starts from the subblock(1731) in backward reference picture (1703) to search for a match (e.g.,the subblock (1741)) in the forward reference picture (1702), and thusdetermines the TMVP (1751). The TMVP (1751) can be considered as an MV(e.g., CorTMV_(L1,0)) that is associated with the backward referencepicture (1703).

In some examples, CorTMV_(L0,i) is associated with a first referencepicture list 0 (L0), and CorTMV_(L1,i) is associated with a secondreference picture list 1 (L1).

In an example, the TMVPs (1751)-(1754) of the respective subblocks(1721)-(1724) can include MVs for bi-prediction, such as shown in FIG.17C. The TMVPs (1751)-(1754) of the respective subblocks (1721)-(1724)can be represented using (i) CorTMV_(L0,i) and (ii) CorTMV_(L1,i) withthe bi-prediction.

TMVPs of the subblocks (1711)-(1714) in the current block (1704) can bedetermined based on the TMVPs of the subblocks (1721)-(1724) in thecorresponding block (1706), respectively. The TMVPs of the subblocks(1711)-(1714) in the current block (1704) can be determined based on MVoffset(s) and the TMVPs of the subblocks (1721)-(1724) in thecorresponding block (1706), respectively. In an example, the TMVPs ofthe subblocks (1711)-1714) in the current block (1704) can be determinedby vector sums of the first offset vector (MVO₁) and the TMVPs of thesubblocks (1721)-(1724) in the corresponding block (1706), respectively,such as shown in Eq. 1.

SbTMV_(L0,i)=MVO₁+CorTMV_(L0,i)

SbTMV_(L1,i)=MVO₁+CorTMV_(L1,i)  Eq. 1

SbTMV_(L0,i) and SbTMV_(L1,i) can represent the TMVPs of the ithsubblock in the current block (1704) that correspond to CorTMV_(L0,i)and CorTMV_(L1,i), respectively. SbTMV_(L0,i) and SbTMV_(L1,i) can beassociated with the forward reference picture (1702) and the backwardreference picture (1703), respectively. In an example, SbTMV_(L0,i) andSbTMV_(L1,i) are associated with L0 and L1, respectively. Eq. 1 can beadapted if the ith subblock is uni-predicted.

A motion field of the current block (1704) can include motioninformation of the subblocks (1711)-(1714). For uni-prediction, theTMVPs of the subblocks (1711)-(1714) can include four vectors (e.g.,SbTMV_(L0,i) or SbTMV_(L1,i) where i is from 0 to 3 corresponding to thesubblocks (1711)-(1714)) and can indicate the motion information of thesubblocks (1711)-(1714). For bi-prediction, the TMVPs of the subblocks(1711)-(1714) can include eight vectors (e.g., SbTMV_(L0,i) andSbTMV_(L1,i) where i is from 0 to 3 corresponding to the subblocks(1711)-(1714)) and can indicate the motion information of the subblocks(1711)-(1714).

A FRUC-based subblock merge candidate, also referred to as a FRUC-basedsubblock TMVP candidate (e.g., a FRUC-based SbTMVP candidate) canindicate the motion field of the current block (1704), for example,including the TMVPs of the subblocks (1711)-(1714). The subblock-basedFRUC described in FIGS. 17A-17C can also be referred to as a FRUC-basedsubblock TMVP mode or a FRUC-based SbTMVP mode.

As described above in FIGS. 15A-15B and FIGS. 17A-17C, the FRUC-basedsubblock TMVP candidate (e.g., described in FIGS. 17A-17C) is determineddifferently from a SbTMVP candidate described in FIGS. 15A-15B. TheFRUC-based subblock TMVP mode described in FIGS. 17A-17C is differentfrom the SbTMVP mode described in FIGS. 15A-15B. The SbTMVP modedescribed in FIGS. 15A-15B can also be referred to as a regular SbTMVPmode to differentiate from the FRUC-based subblock TMVP mode.

FIG. 18A shows another example of the subblock-based FRUC mode, such asthe FRUC-based subblock TMVP mode, which is a variation from theFRUC-based subblock TMVP mode shown in FIG. 17A. The current picture(1701), the current block (1704) including the subblocks (1711)-(1714),the corresponding block (1706) including the subblocks (1721)-(1724),the forward reference picture (1702) and the subblocks (1741)-(1744),the backward reference picture (1703) and the subblocks (1731)-(1734),and the first offset vector (1705) shown in FIG. 18A are described inFIG. 17A.

The TMVPs (1751)-(1754) of the respective subblocks (1721)-(1724) in thecorresponding block (1706) can be determined using the embodiments(e.g., any suitable FRUC process, such as a unidirectional MV estimationor a bidirectional MV estimation) described in FIGS. 16B-16C and17A-17C. In the example shown in FIGS. 18A-18B, TMVPs (1851)-(1854) ofthe subblocks (1711)-(1714) in the current block (1704) are determinedas the TMVPs (e.g., the CorTMV_(L0,i) and/or CorTMV_(L1,i) where i isfrom 0 to 3) (1751)-(1754) of the respective subblocks (1721)-(1724),respectively, as shown in Eq. 2 below.

SbTMV_(L0,i)=CorTMV_(L0,i)

SbTMV_(L1,i)=CorTMV_(L1,i)  Eq. 2

SbTMV_(L0,i) and SbTMV_(L1,i) can represent the TMVPs of the ithsubblock in the current block (1704) that correspond to CorTMV_(L0,i)and CorTMV_(L1,i), respectively. The TMVPs (1751)-(1754) of therespective subblocks (1721)-(1724) can include MVs for uni-prediction,such as shown in FIG. 18B. In FIG. 18B, the TMVPs (1751)-(1754) caninclude CorTMV_(L0,i) or CorTMV_(L1,i) where i is from 0 to 3. The TMVPs(1851)-(1854) of the current block are identical to the TMVPs(1751)-(1754), respectively.

FIG. 18B shows a FRUC-based subblock TMVP candidate (e.g., a FRUC-basedSbTMVP candidate) that indicates a motion field of the current block(1704), for example, including the TMVPs (1861)-(1864) of the subblocks(1711)-(1714).

In some examples, the TMVPs (1751)-(1754) of the respective subblocks(1721)-(1724) can include MVs for bi-prediction. The TMVPs (1751)-(1754)can include CorTMV_(L0,i) and CorTMV_(L1,i) where i is from 0 to 3. TheTMVPs (1851)-(1854) of the current block are identical to the TMVPs(1751)-(1754), respectively.

FIG. 19 shows another example of the subblock-based FRUC mode, such asthe FRUC-based subblock TMVP mode, which is a variation from theFRUC-based subblock TMVP modes shown in FIGS. 17A-17C and 18A-18B. Thecurrent picture (1701), the current block (1704) including the subblocks(1711)-1714), the forward reference picture (1702) and the subblocks(1741)-(1744), and the backward reference picture (1703) and thesubblocks (1731)-(1734) shown in FIG. 19 are described in FIG. 17A.

Initial TMVPs (e.g., CurTMVs) (1951)-(1954) of the respective subblocks(1711)-(1714) in the current block (1704) can be determined using anysuitable FRUC process, such as unidirectional MV estimation(s) and/orbidirectional MV estimation(s) described in FIGS. 16B-16C and 17A-17C.The initial TMVPs (e.g., CurTMVs) (1951)-(1954) can includeCurTMV_(L0,i) and/or CurTMV_(L1,i) where i is an integer from 0 to 3. Inan example, a second offset vector (or a second MVO) can be added to theinitial TMVPs (e.g., CurTMVs) (1951)-(1954) to determine TMVPs (e.g.,SbTMVs) of the respective subblocks (1711)-(1714) in the current block(1704) using Eq. 3.

SbTMV_(L0,i)=MVO₂+CurTMV_(L0,i)

SbTMV_(L1,i)=MVO₂+CurTMV_(L1,i)  Eq. 3

In an example, the second MVO is signaled and parsed. The second MVO canbe identical to or different from the first MVO used in FIGS. 17A-17Cand 18A-18B.

An offset vector (e.g., the first offset vector or the second offsetvector) can be determined as follows. In one embodiment, the offsetvector is a zero vector. The offset vector (being (0, 0)) does not needto be signaled in a bitstream.

In an embodiment, the offset vector can be determined as an offsetvector in a predefined offset vector list. An index can be signaled toindicate which offset vector is selected from the predefined offsetvector list. In an example, the offset vector can be signaled using amethod similar to that used in the MMVD mode to signal an MVD, such asdescribed with reference to Tables 2-3. In an example, a single index issignaled to indicate a magnitude and a direction of the offset vector.In an example, a distance index and a direction index are signaled toindicate the magnitude and the direction of the offset vector. Theoffset vector can be determined based on the index or the indices.

In an embodiment, the offset vector is signaled for the current block inthe bitstream. For example, (i) a magnitude and a direction of theoffset vector or (ii) a x component and a y component of the offsetvector can be signaled in a syntax for the current block.

A TMVP of a first subblock (e.g., (1721)) in the corresponding block(1706) can be determined as below. In an embodiment, the TMVP (e.g.,CorTMV_(L0i) and/or CorTMV_(L1i)) of the first subblock in thecorresponding block (1706) is not available, for example, the TMVP ofthe first subblock cannot be derived by the subblock-based FRUC. In anexample, no TMVP of the first subblock in the corresponding block (1706)is found using a subblock-based FRUC. When the TMVP of the firstsubblock in the corresponding block (1706) is not available, the TMVP ofthe first subblock in the corresponding block (1706) can be generated byone or more TMVPs of neighboring subblock(s), such as a weighted averageof the one or more TMVPs of the neighboring subblock(s). Referring toFIG. 17C, if the TMVP of the subblock (1721) cannot be generated by aFRUC process, the TMVP of the subblock (1721) can be generated based onthe TMVP(s) of the subblock (1722), (1723), and/or (1724).

If the one or more TMVPs of the neighboring subblock(s) are notavailable, a zero MV (e.g., (0, 0)) can be set as the TMVP of the firstsubblock of the corresponding block (1706).

Different positions of the subblocks within the corresponding block(1706) may be used to derive the TMVP of the respective subblock using aFRUC process. In an embodiment, a center position of each subblockwithin the corresponding block (1706) is used to derive the TMVP of therespective subblock using a FRUC process. For example, the TMVP of thefirst subblock in the corresponding block (1706) can be determined basedon an MV passing through the center position in the first subblock. Inan example, the subblock is a 4×4 unit, and thus the center position ofthe 4×4 unit can be a position (1,1), (1,2), (2,1), or (2,2). In anexample, the subblock is an 8×8 unit, and thus the center position ofthe 8×8 unit can be a position (3,3), (3,4), (4,3), or (4,4).

In an embodiment, one of a top-left position, a top-right position, abottom-left position, or a bottom-right position of each subblock withinthe corresponding block (1706) is used to derive the TMVP of therespective subblock using a FRUC process. For example, the TMVP of thefirst subblock in the corresponding block (1706) can be determined basedon an MV passing through one of the top-left position, the top-rightposition, the bottom-left position, or the bottom-right position in thefirst subblock.

The above descriptions related to derivation of the TMVP of the firstsubblock (e.g., (1721)) in the corresponding block (1706) can be appliedto derive an initial TMVP of a subblock (e.g., (1711)) in the currentblock (1704) in FIG. 19 .

The FRUC-based SBTMVP mode may be inferred as true or false based onPOCs of reference pictures and the current picture (1701). In anembodiment, the FRUC-based SBTMVP mode is inferred as false when thePOCs (e.g., in display order) of the reference pictures (e.g., allreference pictures) in L0 and L1 are smaller than the POC of the currentpicture (1701). In an embodiment, the FRUC-based SBTMVP mode is inferredas false when the POCs of the reference pictures (e.g., all of thereference pictures) in L0 and L1 are larger than the POC of the currentpicture (1701).

In an example, a POC of the forward reference picture (1702) is smallerthan the POC of the current picture (1701), and a POC of the backwardreference picture (1703) is larger than the POC of the current picture(1701), and the FRUC-based SBTMVP mode is applied to determine the TMVPsof the subblocks (1711)-(1714) of the current block (1704) as describedin FIGS. 17A-17C, 18A-18B, and 19 .

The FRUC-based subblock TMVP candidate of the current block (1704) suchas shown in FIGS. 17B-17C and 18B can be signaled using any suitablemethod.

In an embodiment, the FRUC-based subblock TMVP candidate may be signaledas a subblock-based candidate used in a subblock-based mode (e.g., asubblock-based merge/skip mode). A subblock candidate list (e.g., asubblock merge/skip candidate list) can be constructed for the currentblock (1704). In an example, multiple subblock-based modes (e.g., theSbTMVP mode, the FRUC-based subblock TMVP mode, and/or an affine mode)share the subblock candidate list. The subblock candidate list (e.g.,the subblock merge/skip candidate list) of the current block (1704) caninclude subblock candidates (e.g., subblock merge candidates), such asthe FRUC-based subblock TMVP candidate, SbTMVP candidate(s) used in theSbTMVP mode (also referred to as a regular SbTMVP mode) in VVC, and thelike. In an example, the subblock candidate list of the current block(1704) includes affine candidate(s), such as affine merge candidate(s)used in an affine merge mode. In an example, the affine mergecandidate(s) include affine inherited candidate(s) and/or affineconstructed candidate(s) that are used in an affine merge/skip mode.

The FRUC-based subblock TMVP mode and the SbTMVP mode (e.g., the regularSbTMVP mode) may be applicable for the current block (1704). Thesubblock candidate list can include the FRUC-based subblock TMVPcandidate and the SbTMVP candidate(s). An index can be signaled at a CUlevel and indicates which subblock candidate is to be applied to thecurrent block (1704). If the index indicates that the FRUC-basedsubblock TMVP candidate is to be used, the current block (1704) is codedusing the FRUC-based subblock TMVP mode, and the TMVPs of the subblocks(1711)-(1714) of the current block (1704) are determined using theFRUC-based subblock TMVP candidate, as described in FIGS. 17A-17C,18A-18B, and 19 .

In an embodiment, the FRUC-based subblock TMVP mode replaces the SbTMVPmode (e.g., the regular SbTMVP mode used in VVC, such as described inFIGS. 15A-15B), and the SbTMVP mode is not allowed for the current block(1704). For example, the subblock candidate list (e.g., the subblockmerge/skip candidate list) of the current block (1704) includes theFRUC-based subblock TMVP candidate and does not include an SbTMVPcandidate.

In an embodiment, the FRUC-based subblock TMVP mode can be used in placeof the SbTMVP mode (e.g., the regular SbTMVP mode such as described inFIGS. 15A-15B) when the FRUC-based subblock TMVP mode is available. TheSbTMVP mode (e.g., the regular SbTMVP mode such as described in FIGS.15A-15B) may be applied only when the FRUC-based subblock TMVP mode isunavailable for the current block (1704).

In an embodiment, whether to enable the FRUC-based subblock TMVP modemay be signaled at a level higher than a block level, such as a slicelevel, a tile level, a tile-group level, a picture level, a sequencelevel, or the like.

In an example, a subblock size of subblocks (e.g., the subblocks(1711)-(1714) and the subblocks (1721)-(1724)) used in the FRUC-basedsubblock TMVP mode may be a pre-defined sub-block size of N×M lumasamples. N and M can be any suitable positive integer. A picture (e.g.,the forward reference picture (1702) or a block (e.g., the current block(1704)) can be partitioned into subblocks having the sub-block size ofN×M luma samples.

In an example, N and M are identical. A block (e.g., the current block(1704)) can be partitioned into subblocks having the sub-block size ofN×N luma samples. When a block width W or a block height H is smallerthan N, the FRUC-based subblock TMVP mode may apply to the block wherethe block can be partitioned as follows. A corresponding subblock widthor a subblock height may be set to the block width W or the block heightH that is smaller than N. If W is smaller than N and H is greater thanor equal to N, the block (e.g., the current block (1704)) can bepartitioned to subblocks having a subblock width of W and a subblockheight of N. If H is smaller than N and W is greater than or equal to N,the block (e.g., the current block (1704)) can be partitioned tosubblocks having the subblock width of N and the subblock height of H.

In an embodiment, when the block width or the block height is smallerthan N, the FRUC-based subblock TMVP mode may not apply for the block.

The motion information of a block (e.g., MVs of subblocks in the block)in a current picture can be determined (e.g., derived) using thesubblock-based FRUC mode instead of being signaled. In thesubblock-based FRUC mode, motion information (e.g., MVs) of thesubblocks in the block can be determined based on motion estimation thattracks motion trajectories between reference subblocks in two respectivereference pictures, such as described in FIGS. 17A-17C, 18A-18B, and 19. For example, in an example of the subblock-based FRUC mode, motioninformation of a subblock (e.g., (1711)) in the block (e.g., (1704)) inthe current picture (e.g., (1701)) is determined based on motionestimation that tracks a motion trajectory between reference subblocks(e.g., (1741) and (1731)) in the two respective reference pictures(e.g., (1702)-(1703)).

FIG. 20 shows a flow chart outlining an encoding process (2000)according to an embodiment of the disclosure. The process (2000) can beused in a video encoder. The process (2000) can be executed by anapparatus for video coding that can include processing circuitry. Invarious embodiments, the process (2000) is executed by the processingcircuitry, such as the processing circuitry in the terminal devices(310), (320), (330) and (340), processing circuitry that performsfunctions of a video encoder (e.g., (403), (603), (703)), or the like.In some embodiments, the process (2000) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (2000). Theprocess starts at (S2001), and proceeds to (S2010).

At (S2010), a corresponding block of a current block in a currentpicture can be determined based on an offset vector. The offset vectorindicates an offset between the current block and the correspondingblock in the current picture. The current block is to be encoded basedon a subblock-based frame-rate up conversion (FRUC) (also referred to asa subblock-based FRUC mode). The current block includes a plurality ofsubblocks.

In an example, the offset vector is a zero vector.

At (S2020), a temporal motion vector predictor (TMVP) of a firstsubblock in the corresponding block can be determined based on asubblock in a forward reference picture of the current picture and asubblock in a backward reference picture of the current picture. Thesubblock in the forward reference picture and the subblock in thebackward reference picture are matched using the subblock-based FRUC.

In an example, a TMVP of a second subblock in the corresponding block isdetermined based on the TMVP of the first subblock in the correspondingblock if the TMPV of the second subblock is not determined by thesubblock-based FRUC. The second subblock neighbors the first subblock.The TMVP of the second subblock in the corresponding block can be usedto determine a second subblock in the current block.

In an example, the TMVP of the first subblock in the corresponding blockis determined based on a motion vector (MV) between the subblock in theforward reference picture and the subblock in the backward referencepicture. The MV passes through one of: a center position, a top-leftposition, a top-right position, a bottom-left position, or abottom-right position in the first subblock in the corresponding block.

In an example, a picture order count (POC) of the forward referencepicture is less than a POC of the current picture and a POC of thebackward reference picture is larger than the POC of the currentpicture.

At (S2030), a TMVP of a subblock in the current block can be determinedbased on the TMVP of the first subblock in the corresponding block.

In an example, the TMVP of the subblock in the current block isdetermined as the TMVP of the first subblock in the corresponding block.

In an example, a motion vector (MV) of the TMVP of the subblock in thecurrent block is determined as a vector sum of the offset vector and arespective MV of the TMVP of the first subblock in the correspondingblock.

At (S2040), the subblock in the current block can be encoded based onthe TMVP of the subblock in the current block.

In an example, an index is encoded and included in a bitstream toindicate the offset vector in a predefined offset vector list.

In an example, the offset vector is encoded and signaled in thebitstream.

The process (2000) then proceeds to (S2099), and terminates.

The process (2000) can be suitably adapted to various scenarios andsteps in the process (2000) can be adjusted accordingly. One or more ofthe steps in the process (2000) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2000). Additional step(s) can be added.

In an embodiment, a subblock merge candidate list includes asubblock-based temporal motion vector prediction (SbTMVP) candidate anda FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block. The current block can be encoded based onthe FRUC-based subblock merge candidate and a subblock merge indexindicating the FRUC-based subblock merge candidate can be encoded andincluded in the bitstream.

In an embodiment, a subblock merge candidate list includes a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The subblock merge candidate list does not include anSbTMVP candidate. The current block can be encoded based on theFRUC-based subblock merge candidate.

If a FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block is available, a subblock merge candidatelist includes the FRUC-based subblock merge candidate and does notinclude a subblock-based temporal motion vector prediction (SbTMVP)candidate. If the FRUC-based subblock merge candidate is not available,the subblock merge candidate list includes the SbTMVP candidate.

A pre-defined subblock size is N×N luma samples. If a width W of thecurrent block is smaller than N and a height H of the current block isgreater than or equal to N, the current block is partitioned intosubblocks having a subblock width of W and a subblock height of N. If His smaller than N and W is greater than or equal to N, the current blockis partitioned into the subblocks having the subblock width of N and thesubblock height of H.

FIG. 21 shows a flow chart outlining a decoding process (2100) accordingto an embodiment of the disclosure. The process (2100) can be used in avideo decoder. The process (2100) can be executed by an apparatus forvideo coding that can include receiving circuitry and processingcircuitry. In various embodiments, the process (2100) is executed by theprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video encoder (403), the processing circuitrythat performs functions of the video decoder (410), the processingcircuitry that performs functions of the video decoder (510), theprocessing circuitry that performs functions of the video encoder (603),and the like. In some embodiments, the process (2100) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(2100). The process starts at (S2101), and proceeds to (S2110).

At (S2110), that a current block including a plurality of subblocks iscoded in a subblock-based frame-rate up conversion (FRUC) mode (alsoreferred to as a subblock-based FRUC) can be determined based on asyntax element in a coded video bitstream. In an example, the codedvideo bitstream includes a current picture that includes the currentblock.

At (S2120), a corresponding block of the current block can be determinedbased on an offset vector. The offset vector indicates an offset betweenthe current block and the corresponding block that is in the currentpicture.

In an example, the offset vector is a zero vector.

In an example, an index is received in the coded video bitstream, andthe offset vector is determined from a predefined offset vector listbased on the index.

In an example, the offset vector is signaled in the coded videobitstream.

At (S2130), a temporal motion vector predictor (TMVP) of a firstsubblock in the corresponding block can be determined based on asubblock in a forward reference picture of the current picture and asubblock in a backward reference picture of the current picture. Thesubblock in the forward reference picture and the subblock in thebackward reference picture are matched using the subblock-based FRUC.

In an example, a TMVP of a second subblock in the corresponding block isdetermined based on the TMVP of the first subblock in the correspondingblock if the TMPV of the second subblock is not determined by thesubblock-based FRUC. The second subblock neighbors the first subblock.The TMVP of the second subblock in the corresponding block can be usedto determine a second subblock in the current block.

In an example, the TMVP of the first subblock in the corresponding blockis determined based on a motion vector (MV) between the subblock in theforward reference picture and the subblock in the backward referencepicture. The MV passes through one of: a center position, a top-leftposition, a top-right position, a bottom-left position, or abottom-right position in the first subblock in the corresponding block.

In an example, a picture order count (POC) of the forward referencepicture is less than a POC of the current picture and a POC of thebackward reference picture is larger than the POC of the currentpicture.

At (S2140), a TMVP of a subblock in the current block can be determinedbased on the TMVP of the first subblock in the corresponding block.

In an example, the TMVP of the subblock in the current block isdetermined as the TMVP of the first subblock in the corresponding block.

In an example, a motion vector (MV) of the TMVP of the subblock in thecurrent block is determined as a vector sum of the offset vector and arespective MV of the TMVP of the first subblock in the correspondingblock.

The process (2100) proceeds to (S2199), and terminates.

The process (2100) can be suitably adapted to various scenarios andsteps in the process (2100) can be adjusted accordingly. One or more ofthe steps in the process (2100) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2100). Additional step(s) can be added.

In an embodiment, a subblock merge candidate list includes asubblock-based temporal motion vector prediction (SbTMVP) candidate anda FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block. The current block can be reconstructedbased on the FRUC-based subblock merge candidate if a subblock mergeindex indicates the FRUC-based subblock merge candidate.

In an embodiment, a subblock merge candidate list includes a FRUC-basedsubblock merge candidate that indicates a TMVP of each subblock in thecurrent block. The subblock merge candidate list does not include anSbTMVP candidate. The current block can be reconstructed based on theFRUC-based subblock merge candidate if a subblock merge index indicatesthe FRUC-based subblock merge candidate.

If a FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block is available, a subblock merge candidatelist includes the FRUC-based subblock merge candidate and does notinclude a subblock-based temporal motion vector prediction (SbTMVP)candidate. If the FRUC-based subblock merge candidate is not available,the subblock merge candidate list includes the SbTMVP candidate.

A pre-defined subblock size is N×N luma samples. If a width W of thecurrent block is smaller than N and a height H of the current block isgreater than or equal to N, the current block is partitioned intosubblocks having a subblock width of W and a subblock height of N. If His smaller than N and W is greater than or equal to N, the current blockis partitioned into the subblocks having the subblock width of N and thesubblock height of H.

FIG. 22 shows a flow chart outlining an encoding process (2200)according to an embodiment of the disclosure. The process (2200) can beused in a video encoder. The process (2200) can be executed by anapparatus for video coding that can include processing circuitry. Invarious embodiments, the process (2200) is executed by the processingcircuitry, such as the processing circuitry in the terminal devices(310), (320), (330) and (340), processing circuitry that performsfunctions of a video encoder (e.g., (403), (603), (703)), or the like.In some embodiments, the process (2200) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (2200). Theprocess starts at (S2201), and proceeds to (S2210).

At (S2210), an initial temporal motion vector predictor (TMVP) of afirst subblock in a current block in a current picture can be determinedbased on a subblock in a forward reference picture of the currentpicture and a subblock in a backward reference picture of the currentpicture. The subblock in the forward reference picture and the subblockin the backward reference picture are matched based on a subblock-basedframe-rate up conversion (FRUC).

At (S2220), a TMVP of the first subblock in the current block can bedetermined based on the initial TMVP of the first subblock in thecurrent block and a motion vector offset (MVO).

In an example, the first subblock in the current block can be encodedbased on the TMVP of the first subblock in the current block.

The process (2200) then proceeds to (S2299), and terminates.

The process (2200) can be suitably adapted to various scenarios andsteps in the process (2200) can be adjusted accordingly. One or more ofthe steps in the process (2200) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2200). Additional step(s) can be added.

FIG. 23 shows a flow chart outlining a decoding process (2300) accordingto an embodiment of the disclosure. The process (2300) can be used in avideo decoder. The process (2300) can be executed by an apparatus forvideo coding that can include receiving circuitry and processingcircuitry. In various embodiments, the process (2300) is executed by theprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video encoder (403), the processing circuitrythat performs functions of the video decoder (410), the processingcircuitry that performs functions of the video decoder (510), theprocessing circuitry that performs functions of the video encoder (603),and the like. In some embodiments, the process (2300) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(2300). The process starts at (S2301), and proceeds to (S2310).

At (S2310), that a current block including a plurality of subblocks iscoded in a subblock-based frame-rate up conversion (FRUC) mode (or asubblock-based FRUC) can be determined based on a syntax element in acoded video bitstream.

In an example, the coded video bitstream includes a current picture isreceived. The current picture includes the current block.

At (S2320), an initial temporal motion vector predictor (TMVP) of afirst subblock in the current block can be determined based on asubblock in a forward reference picture of the current picture and asubblock in a backward reference picture of the current picture. Thesubblock in the forward reference picture and the subblock in thebackward reference picture are matched using the subblock-based FRUC.

At (S2330), a TMVP of the first subblock in the current block can bedetermined based on the initial TMVP of the first subblock in thecurrent block and a motion vector offset (MVO).

In an example, a motion vector (MV) of the TMVP of the first subblock inthe current block is determined as a vector sum of the MVO and arespective MV of the TMVP of the first subblock in the current block.

In an example, an index is received in the coded video bitstream. TheMVO is determined from a predefined MVO list based on the index.

In an example, the MVO is signaled in the coded video bitstream.

The process (2300) proceeds to (S2399), and terminates.

The process (2300) can be suitably adapted to various scenarios andsteps in the process (2300) can be adjusted accordingly. One or more ofthe steps in the process (2300) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2300). Additional step(s) can be added.

Embodiments in the disclosure may be used separately or combined in anyorder. Further, each of the methods (or embodiments), an encoder, and adecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 24 shows a computersystem (2400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 24 for computer system (2400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2400).

Computer system (2400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2401), mouse (2402), trackpad (2403),touch-screen (2410), data-glove (not shown), joystick (2405), microphone(2406), scanner (2407), camera (2408).

Computer system (2400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2410), data-glove (not shown), or joystick (2405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2409), headphones(not depicted)), visual output devices (such as touch-screens (2410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2420) with CD/DVD or the like media (2421), thumb-drive (2422),removable hard drive or solid state drive (2423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2400) can also include an interface (2454) to one ormore communication networks (2455). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (2449) (such as,for example USB ports of the computer system (2400)); others arecommonly integrated into the core of the computer system (2400) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2400) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2440) of thecomputer system (2400).

The core (2440) can include one or more Central Processing Units (CPU)(2441), Graphics Processing Units (GPU) (2442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2443), hardware accelerators (2444) for certain tasks, graphicsadapters (2450), and so forth. These devices, along with Read-onlymemory (ROM) (2445), Random-access memory (2446), internal mass storage(2447) such as internal non-user accessible hard drives, SSDs, and thelike, may be connected through a system bus (2448). In some computersystems, the system bus (2448) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (2448), or through a peripheral bus (2449). In anexample, the touch-screen (2410) can be connected to the graphicsadapter (2450). Architectures for a peripheral bus include PCI, USB, andthe like.

CPUs (2441), GPUs (2442), FPGAs (2443), and accelerators (2444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2445) or RAM (2446). Transitional data can be also be stored in RAM(2446), whereas permanent data can be stored for example, in theinternal mass storage (2447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2441), GPU (2442), massstorage (2447), ROM (2445), RAM (2446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system (2400)having architecture, and specifically the core (2440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2440) that are of non-transitorynature, such as core-internal mass storage (2447) or ROM (2445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   -   JEM: joint exploration model    -   VVC: versatile video coding    -   BMS: benchmark set    -   MV: Motion Vector    -   HEVC: High Efficiency Video Coding    -   SEI: Supplementary Enhancement Information    -   VUI: Video Usability Information    -   GOPs: Groups of Pictures    -   TUs: Transform Units,    -   PUs: Prediction Units    -   CTUs: Coding Tree Units    -   CTBs: Coding Tree Blocks    -   PBs: Prediction Blocks    -   HRD: Hypothetical Reference Decoder    -   SNR: Signal Noise Ratio    -   CPUs: Central Processing Units    -   GPUs: Graphics Processing Units    -   CRT: Cathode Ray Tube    -   LCD: Liquid-Crystal Display    -   OLED: Organic Light-Emitting Diode    -   CD: Compact Disc    -   DVD: Digital Video Disc    -   ROM: Read-Only Memory    -   RAM: Random Access Memory    -   ASIC: Application-Specific Integrated Circuit    -   PLD: Programmable Logic Device    -   LAN: Local Area Network    -   GSM: Global System for Mobile communications    -   LTE: Long-Term Evolution    -   CANBus: Controller Area Network Bus    -   USB: Universal Serial Bus    -   PCI: Peripheral Component Interconnect    -   FPGA: Field Programmable Gate Areas    -   SSD: solid-state drive    -   IC: Integrated Circuit    -   CU: Coding Unit    -   JVET: Joint Video Exploration Team    -   AMVR: Adaptive Motion Vector Resolution    -   POC: Picture Order Count    -   SbTMVP: Subblock-based temporal motion vector prediction

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding in a decoder,comprising: receiving a coded video bitstream comprising a currentpicture, the current picture including a current block, the currentblock including a plurality of subblocks; determining, based on a syntaxelement in the coded video bitstream, that the current block includingthe plurality of subblocks is coded in a subblock-based frame-rate upconversion (FRUC) mode; determining a corresponding block of the currentblock based on an offset vector, the offset vector indicating an offsetbetween the current block and the corresponding block in the currentpicture; determining a temporal motion vector predictor (TMVP) of afirst subblock in the corresponding block based on a subblock in aforward reference picture of the current picture and a subblock in abackward reference picture of the current picture, the subblock in theforward reference picture and the subblock in the backward referencepicture being matched using the subblock-based FRUC mode; anddetermining, based on the TMVP of the first subblock in thecorresponding block, a TMVP of a subblock in the plurality of subblocksin the current block.
 2. The method of claim 1, wherein the determiningthe TMVP of the subblock in the plurality of subblocks in the currentblock comprises: determining the TMVP of the subblock in the pluralityof subblocks in the current block as the TMVP of the first subblock inthe corresponding block.
 3. The method of claim 1, wherein thedetermining the TMVP of the subblock in the plurality of subblocks inthe current block comprises: determining a motion vector (MV) of theTMVP of the subblock in the plurality of subblocks in the current blockas a vector sum of the offset vector and a respective MV of the TMVP ofthe first subblock in the corresponding block.
 4. The method of claim 1,wherein the offset vector is zero.
 5. The method of claim 1, furthercomprising: receiving an index in the coded video bitstream; anddetermining the offset vector from a predefined offset vector list basedon the index.
 6. The method of claim 1, wherein the offset vector issignaled in the coded video bitstream.
 7. The method of claim 1, furthercomprising: determining a TMVP of a second subblock in the correspondingblock based on the TMVP of the first subblock in the corresponding blockin response to the TMVP of the second subblock not being determined bythe subblock-based FRUC mode, the second subblock neighboring the firstsubblock.
 8. The method of claim 1, wherein the determining the TMVP ofthe first subblock in the corresponding block comprises: determining theTMVP of the first subblock in the corresponding block based on a motionvector between the subblock in the forward reference picture and thesubblock in the backward reference picture, the motion vector passingthrough one of: a center position, a top-left position, a top-rightposition, a bottom-left position, or a bottom-right position in thefirst subblock in the corresponding block.
 9. The method of claim 1,wherein a picture order count (POC) of the forward reference picture isless than a POC of the current picture and a POC of the backwardreference picture is larger than the POC of the current picture.
 10. Themethod of claim 1, wherein a subblock merge candidate list includes asubblock-based temporal motion vector prediction (SbTMVP) candidate anda FRUC-based subblock merge candidate that indicates a TMVP of eachsubblock in the current block; and the method includes reconstructingthe current block based on the FRUC-based subblock merge candidate inresponse to a subblock merge index indicating the FRUC-based subblockmerge candidate.
 11. The method of claim 1, wherein a subblock mergecandidate list includes a FRUC-based subblock merge candidate thatindicates a TMVP of each subblock in the plurality of subblocks in thecurrent block, the subblock merge candidate list not including asubblock-based temporal motion vector prediction (SbTMVP) candidate; andthe method includes reconstructing the current block based on theFRUC-based subblock merge candidate in response to a subblock mergeindex indicating the FRUC-based subblock merge candidate.
 12. The methodof claim 1, wherein in response to a FRUC-based subblock merge candidatethat indicates a TMVP of each subblock in the current block beingavailable, a subblock merge candidate list includes the FRUC-basedsubblock merge candidate and does not include a subblock-based temporalmotion vector prediction (SbTMVP) candidate; and in response to theFRUC-based subblock merge candidate not being available, the subblockmerge candidate list includes the SbTMVP candidate.
 13. The method ofclaim 1, wherein a pre-defined subblock size is N×N luma samples; inresponse to a width W of the current block being smaller than N and aheight H of the current block being greater than or equal to N, themethod further includes partitioning the current block into subblockshaving a subblock width of W and a subblock height of N; and in responseto H being smaller than N and W being greater than or equal to N, themethod further includes partitioning the current block into thesubblocks having the subblock width of N and the subblock height of H.14. A method of video decoding in a decoder, comprising: receiving acoded video bitstream comprising a current picture, the current pictureincluding a current block, the current block including a plurality ofsubblocks; determining, based on a syntax element in the coded videobitstream, that the current block including the plurality of subblocksis coded in a subblock-based frame-rate up conversion (FRUC) mode;determining an initial temporal motion vector predictor (TMVP) of afirst subblock in the plurality of subblocks in the current block basedon a subblock in a forward reference picture of the current picture anda subblock in a backward reference picture of the current picture, thesubblock in the forward reference picture and the subblock in thebackward reference picture being matched based on the subblock-basedFRUC mode; and determining, based on the initial TMVP of the firstsubblock in the plurality of subblocks in the current block and a motionvector offset (MVO), a TMVP of the first subblock in the plurality ofsubblocks in the current block.
 15. The method of claim 14, wherein thedetermining the TMVP of the first subblock in the plurality of subblocksin the current block comprises: determining a motion vector (MV) of theTMVP of the first subblock in the plurality of subblocks in the currentblock as a vector sum of the MVO and a respective MV of the TMVP of thefirst subblock in the plurality of subblocks in the current block. 16.The method of claim 14, further comprising: receiving an index in thecoded video bitstream; and determining the MVO from a predefined MVOlist based on the index.
 17. The method of claim 14, wherein the MVO issignaled in the coded video bitstream.
 18. The method of claim 14,further comprising: determining an initial TMVP of a second subblock inthe plurality of subblocks in the current block based on the initialTMVP of the first subblock in the plurality of subblocks in the currentblock in response to the initial TMVP of the second subblock not beingdetermined by the subblock-based FRUC mode, the second subblockneighboring the first subblock.
 19. The method of claim 14, wherein asubblock merge candidate list includes a subblock-based temporal motionvector prediction (SbTMVP) candidate and a FRUC-based subblock mergecandidate that indicates a TMVP of each subblock in the plurality ofsubblocks in the current block; and the method includes reconstructingthe current block using the FRUC-based subblock merge candidate inresponse to a subblock merge index indicating the FRUC-based subblockmerge candidate.
 20. The method of claim 14, wherein a subblock mergecandidate list includes a FRUC-based subblock merge candidate thatindicates a TMVP of each subblock in the plurality of subblocks in thecurrent block, the subblock merge candidate list not including asubblock-based temporal motion vector prediction (SbTMVP) candidate; andthe method includes reconstructing the current block using theFRUC-based subblock merge candidate in response to a subblock mergeindex indicating the FRUC-based subblock merge candidate.